(1) Field of the Invention
The present invention relates to a laminated photosensitive material for electrophotography. More particularly, the present invention relates to a laminated photosensitive material for electrophotography, which has a very high sensitivity and a high initial charge voltage in combination.
(2) Description of the Prior Art
An organic polymeric photoconductor such as polyvinyl carbazole has properties suitable for formation of photosensitive layers, such as high transparency, good flexibility and good film-forming property, but this photoconductor is not satisfactorily used in the field of commercial electrophotographic reproduction because the sensitivity is low.
As means for improving the sensitivity, there has already been proposed a method in which polyvinyl carbazole (often referred to as "PVK" hereinafter) is used as a material of a laminated photosensitive plate. As a typical instance of such proposal, there can be mentioned a method an undercoat layer of a composition comprising polyvinyl carbazole and photoconductive zinc oxide is formed on a conductive substrate and a topcoat layer of polyvinyl carbazole is formed on this undercoat layer.
A laminated photosensitive plate prepared according to this method has a sensitivity higher than that of a photosensitive plate of PVK alone or a photosensitive plate formed of a composition of PVK and zinc oxide. However, this laminated photosensitive plate is still insufficient in attainment of the object of forming an image having a high density and a high contrast. More specifically, at the step of charging by corona discharge or the like, the surface saturation voltage of this laminated photosensitive plate is about 200 V at highest, and therefore, it is very difficult to form an electrostatic latent image having a high density and a high contrast.